Insomnia is often comorbid with obstructive sleep apnea. It reduces positive airway pressure (PAP) therapy acceptance and adherence. Comorbid patients show greater daytime impairments and poorer health outcomes. The insomnia often goes undiagnosed, undertreated, or untreated. Pharmacotherapy is not recommended for long-term treatment. Although care should be taken administering behavioral therapies to patients with elevated sleepiness, cognitive behavior therapy for insomnia (CBTi) is an effective and durable nondrug therapy that reduces symptoms and may increase the effectiveness of PAP therapy. Sleep clinics should be alert to comorbid insomnia and provide adequate diagnostic tools and clinicians with CBTi expertise.